Optical disks are an increasingly popular medium for digitally storing information. Information is stored in binary format, with binary zeros represented by non-reflective pits stamped into a plastic disk and binary ones represented by reflective high points on the disk. The data is retrieved by an optical head which directs a laser source onto the surface of the disk and which utilizes a light sensitive photo diode to detect light reflecting from the disk surface. The binary information is converted to electrical signals and decoded into audio and/or video output.
In present large-scale optical disk storage and retrieval systems each disk is installed in a separate cartridge having a separate drive. Each cartridge is comprised of an enclosed casing which includes the disk and all of the components, including the drive mechanism, optical head, and electronics, which are necessary for retrieving the data from the disk. The cartridges are installed into the storage system via a slot in the system and are multiplexed to the central processing unit.
These disk cartridges are square in shape and have two large square faces which correspond to the top and bottom of the disk, and four thin rectangular faces which surround the disk. On one of the four faces is a shutter. The shutter provides a port through which the cartridge is interfaced to the central processing unit.
Many mass storage library systems require that the cartridge be inserted into the system shutter side last, which is opposite to the direction made customary by devices such as video cassette recorders and audio cassettes. Others allow for introduction of the shutter first, but rely on complex systems of cams and gears to rotate the cartridge for pick up by the cartridge selection mechanism of the library system.